This invention relates to a high-intensity LED epitaxial substrate, which is of the type having a double-hetero structure, manufactured by joint use of vapor phase epitaxy (an MOCVD process or MBE process) and liquid phase epitaxy (an LPE process), and to a method of manufacturing the substrate.
In order to epitaxially grow a substrate for, say, a red-light emitting high-intensity LED in the prior art, first a p-type layer of Al.sub.0.75 Ga.sub.0.25 As is formed as a p-type cladding layer to a thickness of 200 microns on a p-type GaAs substrate [(100) surface] by the LPE process. This is followed by forming a p-type Al.sub.0.35 Ga.sub.0.65 As layer as a p-type active layer to a thickness of 2-3 microns, and then an n-type Te-doped Al.sub.0.75 Ga.sub.0.25 As layer as an n-type cladding layer to a thickness of 50 microns. Next, a GaAs substrate-selective etchant (e.g., NH.sub.4 OH:H.sub.2 O.sub.2 =1.7) is used to remove the light-absorptive GaAs substrate, thereby providing a high-intensity LED chip.
Though the LPE process exhibits a high growth rate and therefore is suitable for forming layers that are thick, it is difficult to control thickness and carrier concentration. Consequently, when an epitaxial substrate having a double-hetero structure is fabricated solely by the LPE process, a variance in thickness and carrier concentration within the wafer surface tends to occur when the active layer is formed. As a result, stable luminance cannot be obtained.
Furthermore, attempting to grow a mechanically strong and thick (about 200 microns) mixed-crystal substrate solely by the MOCVD or MBE process is impractical since it involves a prolonged period of time and high cost.